Techniques for releasing parts in additive fabrication and related systems and methods

ABSTRACT

An improved additive fabrication device and a build platform are provided. The additive fabrication device is configured to form layers of material on a build surface. The additive fabrication device comprising: a build platform comprising: a rigid structure; an actuation structure attached to the rigid structure, wherein the actuation structure comprises one or more sheet handles and a flexible sheet, and wherein a first surface of the flexible sheet forms a build surface on which the additive fabrication device is configured to form layers of materials; and the one or more sheet handles are configured to be actuated to apply a force to the flexible sheet while at least a part of the actuation structure remains attached to the rigid structure, to deform at least a part of the flexible sheet away from the rigid structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. § 119(e) ofU.S. Provisional Patent Application No. 63/214,884, filed Jun. 25, 2021,titled “Techniques for Releasing Parts in Additive Fabrication andRelated Systems and Methods,” which is hereby incorporated by referencein its entirety.

FIELD OF INVENTION

The present invention relates generally to systems and methods forreleasing additively fabricated parts from a build platform in anadditive fabrication device.

BACKGROUND

Additive fabrication, e.g., 3-dimensional (3D) printing, providestechniques for fabricating objects, typically by causing portions of abuilding material to solidify at specific locations. Additivefabrication techniques may include stereolithography, selective or fuseddeposition modeling, direct composite manufacturing, laminated objectmanufacturing, selective phase area deposition, multi-phase jetsolidification, ballistic particle manufacturing, particle deposition,laser sintering or combinations thereof. Many additive fabricationtechniques build parts by forming successive layers, which are typicallycross-sections of the desired object. Typically, each layer is formedsuch that it adheres to either a previously formed layer or a buildsurface upon which the object is built.

In one approach to additive fabrication, known as stereolithography(SLA), solid objects are created by successively forming thin layers ofa curable polymer resin, typically first onto a build surface and thenone on top of another. Exposure to actinic radiation cures a thin layerof liquid resin, which causes it to harden and adhere to previouslycured layers or the bottom surface of the build surface.

In another approach to additive fabrication, known as selective lasersintering (SLS), solid objects are produced from laser-fusible powder ina layer-wise fashion. During SLS, thin layers of powder are successivelydistributed across a build platform (e.g., through a powder roller).Laser energy is directed to a respective layer of powder to fuse, melt,or sinter selected regions of the laser-fusible powder to form across-section of a solid object. This process is repeated as additionallayers of powder are distributed and the layer energy is used to fusesuccessive cross-sections of the solid object.

In another approach to additive fabrication, known as fused depositionmodeling (FDM), filament-shaped material is heated and extruded througha nozzle, and positioned on a build platform or stacked on previouslydeposited materials accordingly to fabricate a three-dimensional object.

In another approach to additive fabrication, known as binder jetting, anink jet head sprays a binder onto successive thin layers of powder,which, when cured, forms regions of power held together by the binderthat represents a given cross-section of the object to be fabricated.

In another approach to additive fabrication, known as inkjet printing,an inkjet printing head nozzle sprays polymerizable compositions onto abuild platform in consecutive layers. Each layer is cured and solidifiedusing a suitable methodology (e.g., UV light) to form a givencross-section of the object to be fabricated.

SUMMARY

According to some aspects, a build platform configured to be removablyattached to an additive fabrication device is provided, the buildplatform comprising a rigid structure, and an actuation structurecoupled to the rigid structure and comprising one or more sheet handlesand a flexible sheet, wherein the one or more sheet handles are attachedto the flexible sheet, wherein a first surface of the flexible sheetforms a build surface on which the additive fabrication device isconfigured to form layers of material, and wherein the one or more sheethandles are configured to be actuated to deform at least a part of theflexible sheet away from the rigid structure.

According to some aspects, an additive fabrication device configured toform layers of material on a build surface is provided, the additivefabrication device comprising a build platform comprising a rigidstructure, and an actuation structure coupled to the rigid structure andcomprising one or more sheet handles and a flexible sheet, wherein theone or more sheet handles are attached to the flexible sheet, wherein afirst surface of the flexible sheet forms a build surface on which theadditive fabrication device is configured to form layers of material,and wherein the one or more sheet handles are configured to be actuatedto deform at least a part of the flexible sheet away from the rigidstructure.

The foregoing apparatus and method embodiments may be implemented withany suitable combination of aspects, features, and acts described aboveor in further detail below. These and other aspects, embodiments, andfeatures of the present teachings can be more fully understood from thefollowing description in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Various aspects and embodiments will be described with reference to thefollowing figures. It should be appreciated that the figures are notnecessarily drawn to scale. In the drawings, each identical or nearlyidentical component that is illustrated in various figures isrepresented by a like numeral. For purposes of clarity, not everycomponent may be labeled in every drawing.

FIGS. 1A-1C illustrate an exemplary build platform in differentconfigurations suitable for use in an additive fabrication device,according to some embodiments.

FIGS. 2A-2C illustrate components of an exemplary actuation structure ofthe build platform, according to some embodiments.

FIGS. 3A-3C illustrate an exemplary rigid structure of the buildplatform in different perspectives, according to some embodiments.

FIG. 4 illustrates an exemplary trough design on a rigid structure thatengages with handle rods of an actuation structure, according to someembodiments.

FIGS. 5A-5D illustrate an exemplary process in which an actuationstructure actuates to release fabricated parts from a build platform,according to some embodiments.

FIG. 6 illustrates an exemplary mount on which a built platform ismounted to remove fabricated parts from the build platform, according tosome embodiments.

FIGS. 7A-7I illustrate exemplary dripping-prevention designs of anactuation structure, according to some embodiments.

FIGS. 8A-8B depict an illustrative stereolithographic additivefabrication device, according to some embodiments; and

FIG. 9 depicts an illustrative selective laser sintering additivefabrication device, according to some embodiments.

DETAILED DESCRIPTION

In additive fabrication, irrespective of the particular mechanism bywhich layers of material are formed, the material is usually formed onsome kind of surface usually referred to as a “build surface.” The buildsurface is typically the surface of a component of the additivefabrication device referred to as a “build platform.” The build platformmay, in some additive fabrication devices, be configured to move withinthe device so that material can be deposited at an appropriate positionon the build surface. For instance, build platforms are frequentlyconfigured to move in a vertical direction between formation of eachlayer so that a new layer may be formed on top of a previously formedlayer.

Typically, a first layer of material is formed on the build surface asan initial step of the formation process. The first layer may providestability for subsequent formation of additional layers and/or mayprovide a layer through which a part being formed may be adhered to thebuild surface. The degree to which the first layer and the build surfaceadhere to one another may depend on multiple factors, such as thematerial used to form the layer, the material of the build surface, andthe geometries of the build platform and/or the first layer. In somecases, the first layer of the part being fabricated may have an areathat is sufficiently small that the adhesive forces between the firstlayer and the build surface during fabrication may be insufficient toretain contact between the part and build surface, which may lead to thepart separating partially or completely from the build surface. Assumingthe part successfully adheres to the build surface throughout thefabrication process, however, it is removed from the build surface as apost-processing step subsequent to fabrication of the part beingcompleted.

In addition to removal of a part from a build surface, additionalpost-processing steps may be performed subsequent to fabrication of thepart. In some use cases, support material may have been formed for thepurpose of mechanically supporting overhanging or otherwise unsupportedstructures of the part during fabrication, and this excess material maybe removed (e.g., using a knife or other cutting tool). In some usecases, cleaning of a part may be performed after fabrication. Forexample, when using a photopolymer-based additive fabrication device itmay be beneficial to immerse a newly formed part into a cleaningsolution such as isopropyl alcohol to remove excess uncured or partiallycured resin from surfaces of the newly formed part. In some use cases,the surface of a fabricated part may be altered or finished usingtechniques that etch or otherwise affect the surface characteristics ofthe part. For example, parts fabricated using a fused filament additivefabrication technology may be finished using a vapor polishing technique(e.g., using acetone vapor) which causes the surface of the part to besmoothed and appear glossy. In some use cases, a part may be immersed inwater and/or an acid/alkaline solution (e.g., sodium hydroxide) todissolve a portion of the part.

Performing post-processing steps, including but not limited to thosediscussed above, may, however, risk damage to the fabricated part. Inmany cases, fabricated parts can be fragile and may include featuresthat could be damaged and/or removed by certain post-processing steps.For example, a user removing a support structure from a part or cleaninga part may exert a sufficient force upon the part (e.g., through holdingor otherwise) that the force causes the part to be damaged. In somecases, removing a part from a build surface to which it is adhered maycause damage to the part via the forces that are necessarily exerted onthe part in order to remove it. In some extreme cases, the use of ascraping or cutting tool to remove a part from a build surface mayresult in injury to a user. For example, if the adhesive forces betweena fabricated part and a build surface are sufficiently high, the usermay have to exert considerable force in order to separate the part fromthe build surface, which increases the risk of injury.

As a result of these and other challenges with post-processing, it maybe desirable to reduce adhesive forces between the part and the buildplatform during fabrication to make it easier to perform post-processingof parts after fabrication. However, such a reduction may cause a partto separate partially or fully from the build platform duringfabrication, typically causing the fabrication process to fail.Consequently, conventional processes and devices retain high adhesiveforces between the part and the build platform to ensure successfulfabrication yet resulting in post-processing challenges such as theaforementioned examples.

The inventors have recognized and appreciated that removal of a partfrom a build surface may be performed using one or more removalmechanisms that, when actuated, deform the build surface thereby causingthe part to separate from the build platform. The build surface may be,or may comprise, the surface of a flexible build layer that is fixed tothe build platform in part whilst some portions of the flexible buildlayer may be free to move relative to a base portion of the buildplatform. For example, a build layer may be removably attached to a baseof the build platform through magnetic force. The removal mechanism mayinclude any mechanism that, when actuated, applies a force onto thebuild layer in a direction away from a base of the build platform towhich the build layer is attached. The removal mechanism thereby causesthe build layer (and thereby the build surface) to deform, which in turnmay cause a part adhered to the build surface to separate from it.

According to some embodiments, a removal mechanism may comprise one ormore elements that can be moved relative to (e.g., towards and awayfrom) the build surface, such that actuating the mechanism causes theone or more elements to push at least a portion of the build surfaceaway from the base to which the build surface is attached. Actuation ofthe mechanism may be manual, such as via a handle that can be pushed bya user holding the build platform, and/or may be automatic, such as viaone or more motors that operate to move the elements to push the buildsurface.

According to some embodiments, a build platform may include one or moremechanisms, in addition to the removal mechanism(s), that apply arestorative force to the build layer. Since a flat build surface isdesirable for fabrication, such a restorative mechanism may act toreturn the build surface to a flat state after the removal mechanism isused to deform the build surface to remove a part. An illustrative usecase for a build platform so configured may, therefore, comprise acts offabricating a part on a flat build surface of a build platform,actuating a removal mechanism to deform the build layer and therebyseparate the part from the build platform, then manipulating the removalmechanism such that its force upon the build layer is sufficientlyreduced that a restorative mechanism can act to return the build surfaceto a flat state. A restorative mechanism therefore includes any elementsof the build platform that act to apply a force onto the build layer toreturn the build surface to a flat state.

In some embodiments, as an alternative to a restorative mechanism, thebuild layer may be formed from material that naturally returns to a flatstate when the removal mechanism is suitable actuated away from thebuild surface. For example, the build layer may comprise a rigidmaterial that buckles when force is applied to it by the removalmechanism, but that flexes back to its original state when the removalmechanism stops applying such a force.

According to some embodiments, a build platform of an additivefabrication device may be removable from the device. In some cases, thebuild platform containing one or more removal mechanisms may beconfigured to be attached to portions of the additive fabrication deviceduring fabrication and then removed from the device after fabrication.Separation of a part from the build platform may therefore, in at leastsome cases, occur when the build platform is separated from the additivefabrication device.

A build platform configured to be removably attached to an additivefabrication device may, in some embodiments, comprise a rigid structure,an actuation structure attached to the rigid structure, wherein theactuation structure comprises one or more sheet handles and a flexiblesheet. For example, the flexible sheet may comprise one or more magneticmaterials (e.g., ferromagnetic materials such as iron, steel, stainlesssteel, etc.). In another example, the flexible sheet may be made be ofnon-magnetic materials but include magnetic materials such as magnetictape attached to it.

In some embodiments, the actuation structure may include two sheethandles attached to opposite sides of a flexible sheet. In someembodiments, the sheet handles and the flexible sheet are separatecomponents and are joined together through fastening means such as nutsand bolts, pins and rivets, welding, glue, crimps, snap-fits,shrink-fits, etc. Alternatively, the sheet handles and the flexiblesheet are an integrated part and are manufactured from the samematerial, and wherein a first surface of the flexible sheet forms abuild surface on which the additive fabrication device is configured toform layers of materials, and the one or more sheet handles areconfigured to be actuated (e.g., either manually by a user or throughmotorized means) to apply a force to the flexible sheet, to deform atleast a part of the flexible sheet away from the rigid structure.

In some embodiment, during the actuation of the one or more sheethandles, part of the flexible sheet (e.g., the central portion)experiences an elastic force (e.g., due to the “squeezing” of the sheethandles) that is greater than the magnetic force exerted on it by therigid structure. As a result, the part of the flexible sheet deforms andbends away from the rigid structure. At the same time, other parts ofthe flexible sheet (e.g., edges of the flexible sheet where the sheethandles are attached) experience an elastic force that is smaller thanthe magnetic force exerted by the rigid structure (or the magnetic forceplus normal force due to the edge parts of the flexible sheet resting introughs of the rigid structure). In some embodiments, the magneticmaterials placed along the edge of the rigid structure (the edges wherethe sheet handles are attached to the flexible sheet) exert greatermagnetic force than the magnetic materials placed in the center regionof the rigid structure).

In some embodiments, the actuation structure is attached to the rigidstructure through magnetic force.

In some embodiments, a second surface of the flexible sheet isconfigured to be attached to a first surface of the rigid structure, andwherein the first surface of the rigid structure includes: a firstmagnetic zone exerting a first amount of magnetic force per area on theactuation structure, and a second magnetic zone exerting a second mountof magnetic force per area on the actuation structure; and wherein thefirst amount is different from the second amount.

In some embodiments, the one or more sheet handles include two sheethandles respectively attached to the flexible sheet at opposite sides ofthe flexible sheet.

In some embodiments, the rigid structure includes a mounting device(e.g., top handle and a “dovetail”) configured to be attached to theadditive fabrication device.

In some embodiments, the one or more sheet handles each comprises adrip-prevention structure to prevent liquid on the flexible sheet fromdripping down the sheet handles. The dripping resin occurs when thebuild platform is oriented such that the flexible sheet is above therigid structure and the sheet handles.

In some embodiments, the build platform is configured to be removed fromthe additive fabrication device and to be attached to a positional tool(e.g., a jig) for the actuation of the one or more sheet handles.

In some embodiments, the orientation of the positional tool isadjustable. In some embodiments, the positional tool can be orientedsuch that the build platform is attached to the positional tool at anangle. As a result, after the actuation of one or more sheet handles,the fabricated parts slide down the flexible sheet due to gravity.

In some embodiments, the rigid structure includes troughs at the edgesand parts of the one or more sheet handles rest in the troughs. Thetroughs act as a locating feature for the build surface, an area whereadditional magnetic force can be applied to aid in adhesion of theactuation structure to the rigid structure towards the edges of thebuild platform, and a place for the surface rods to pivot for the camfeature.

In some embodiments, during actuation of the one or more handles toapply a force to the flexible sheet, during a first phase of theactuation, an elastic force experienced by a first part (e.g., thecenter portion) of the flexible sheet is smaller than the magnetic forceexerted on the first part of the flexible sheet (as a result, theflexible sheet stays in contact with the rigid structure); during asecond phase of the actuation, the elastic force experienced by thefirst part of the flexible sheet is greater than the magnetic forceexerted on the first part of the flexible sheet (thereby causing thefirst part of the flexible sheet to move away from the rigid structure).

In some embodiments, the one or more sheet handles are configured to beactuated while at least a part of the actuation structure remainsattached to the rigid structure.

In some embodiments, the actuation structure is attached to the rigidstructure through mechanical retaining means.

Following below are more detailed descriptions of various conceptsrelated to, and embodiments of, techniques for separating an additivelyfabricated part from a build surface. It should be appreciated thatvarious aspects described herein may be implemented in any of numerousways. Examples of specific implementations are provided herein forillustrative purposes only. In addition, the various aspects describedin the embodiments below may be used alone or in any combination, andare not limited to the combinations explicitly described herein. Inparticular, while the following describes embodiments in which removalmechanisms and/or restorative mechanisms may be located within a buildplatform, it may be appreciated that one or more components of suchmechanisms may be located within an additive fabrication device inproximity to the build platform and the same results achieved so long asthe appropriate forces, described below, can be directed to the buildsurface.

FIGS. 1A-1C illustrate an exemplary build platform 100 in differentconfigurations suitable for use in an additive fabrication device,according to some embodiments. For example, the build platform 100 maybe suitable for use in a stereolithography (SLA) additive fabricationdevice as described in FIGS. 8A-8B, or for use in a selective lasersintering (SLS) additive fabrication device as described in FIG. 9 . Ata high level, the build platform 100 includes two parts: a rigidstructure 102, which comprises a top handle 106 and a mountingattachment 104; and an actuation structure 108, which comprises aflexible sheet 112 and sheet handles 110. The actuation structure can beremovably attached to the rigid structure as described further below.FIG. 1A depicts the actuation structure attached to the rigid structure,whereas FIG. 1B depicts the actuation structure separately from therigid structure. FIG. 1C depicts the depicts the actuation structureattached to the rigid structure with the actuation structure having beenactuated to deform the flexible sheet of the actuation structure.

FIG. 1A illustrates the build platform 100 in an initial configurationwherein a rigid structure 102 is attached to an actuation structure 108.In this configuration, a flexible sheet 112 of the actuation structure108 sits substantially flush against the bottom surface of the rigidstructure 102, and sheet handles 110 of the actuation structure abutopposite sides of rigid structure 102. As will be described in moredetail below, in some embodiments, the flexible sheet 112 may beattached to the bottom surface of rigid structure 102 by varioustechniques, which may include magnetic forces between the sheet and thestructure. The bottom surface of the flexible sheet may be referred toherein as the “build surface” of the build platform 100, being a surfaceon which layers of materials will be successively placed duringfabrication of parts. The bottom surface of the rigid structure 102includes troughs 114 of predetermined curvature at opposite edges toengage with handle rods 116 of the sheet handles, as the flexible sheet112 sits flush against the bottom surface of the rigid structure 102.The build platform 100 may be placed in post-processing devices such asa wash station or a curing station, or be mounted on a mount (e.g., ajig) for fabricated parts removal using the mounting attachment 104.

FIG. 1B illustrates a second configuration of the build platform 100where the rigid structure 102 is detached from the actuation structure108. This configuration may occur, for example, when a user detaches theactuation structure 108 from the rigid structure 102 for cleaning ormaintenance. In some embodiments, to minimize downtime of an additivefabrication device, the user may swap the actuation structure 108,having fabricated parts on the build surface after a fabrication processhas completed, with another actuation structure 108 having a clean buildsurface.

FIG. 1C illustrates a third configuration of build platform 100 wherethe sheet handles 110 of the actuation structure 108 have been actuatedto apply a force to the flexible sheet 112, causing the sheet to deform.The deformation of the flexible sheet 112 may allow fabricated partsattached to the flexible sheet 112 (parts not shown in FIG. 1C) to bemore easily peeled off the build surface than would be possible from arigid, planar build platform.

In the example of FIG. 1C, the build platform 100 may comprise one ormore restorative mechanisms configured to apply a force to restore theactuation structure 108 to its original configuration as shown in FIG.1A (that is, with the flexible sheet being flat, or substantially flat,against the bottom surface of the rigid structure 102). In someembodiments, the restorative mechanism may be configured so that theforce applied to the actuation structure is sufficiently large when thesheet handles are positioned in the actuated position as shown in FIG.1C to move the actuation structure 108 back against the rigid structure(so long as the user applies a force onto the handles that is lower thanthe force applied by the restorative mechanism). For example, therestorative mechanism may be configured so that once the user lets go ofthe handles, the actuation structure 108 will be pulled back onto therigid structure. In some embodiments, the restorative mechanism may beconfigured so that the force applied to the actuation structure is onlylarge enough to pull the actuation structure 108 back against the rigidstructure when the actuation structure is moved partially back towardthe rigid structure by the user moving the handles back to theiroriginal position shown in FIG. 1A. For example, the restorativemechanism may be configured so that once the user begins to move thehandles back to their original position, the force applied by therestorative mechanism pulls the actuation structure onto the rigidstructure. In either case, once the actuation structure is pulled backto the rigid structure, the restorative mechanism may be configured tomaintain the actuation structure in that position until a sufficientlyhigh force is applied by the sheet handles 110 to overcome the force ofthe restorative mechanism.

As will be described in more detail below, during actuation of theactuation structure, at least part of the sheet handles 110 (e.g., thehandle rods) are slidingly attached to the troughs 114 of the rigidstructure 102, as a central portion of the flexible sheet 112 begins toseparate from the bottom surface of the rigid structure 102. As aresult, during actuation, each of the sheet handles 110 pivots towardsthe top handle 106 around the troughs 114. In some embodiments, the tophandle 106 limits the maximum distance sheet handles 110 can travel.

In some embodiments, the flexible sheet 112 is formed from one or morematerials such that the build surface (e.g., the bottom surface of theflexible sheet 112) is flexible or otherwise deformable. In someembodiments, the flexible sheet 112 may comprise a ferromagnetic layer,such as spring steel. In some embodiments, additional layers may beadded to such a ferromagnetic layer. For example, protective coatingsand/or other materials may be disposed upon the ferromagnetic layer thatmodify forces of adhesion between the build surface and material formedon the build surface.

In some embodiments, when the actuation structure 108 is attached to thebuild platform, the flexible sheet 112 may be attached to rigidstructure 102 at one or more locations so long as at least some of thebuild layer is free to move or deform such that the build surfacechanges shape. In some embodiments, the flexible sheet 112 may beremovably attached to the bottom surface of rigid structure 102. Forinstance, rigid structure 102 may include a magnetic element ofsufficient strength embedded below the bottom surface to hold flexiblesheet 12 in place during fabrication whilst allowing a user to separatethe build layer from the rigid body via application of force on thesheet handles 110.

In some embodiments, the restorative mechanism applies a force to theflexible sheet 112 to cause the flexible sheet 112 to adopt asubstantially conformal shape when the actuation structure 108 isattached to the rigid structure 102. In some cases, such a shape mayresult in the build surface being flat against the rigid structure 102as seen in FIG. 1A. For example, the restorative mechanism may includethe restoring elastic force of the flexible sheet 112, or magnetsembedded in the bottom surface of the rigid structure 102 that attractthe flexible sheet 112. In some embodiments, restorative forces appliedby the restorative mechanism may be applied across any portion of thebuild surface, such as the entire surface or only a portion of the buildsurface on which material is expected to be formed during additivefabrication. In some embodiments, the restorative mechanism may comprisea single restorative force producing element (e.g., a single magnet) ormay comprise multiple restorative force producing elements that eachproduce restorative forces, which need not necessarily be of the samemagnitude nor produced by the same means (e.g., the restorativemechanism may comprise any number of magnets and/or springs coupled tothe build layer).

In some embodiments, the restorative mechanism may include components inboth the rigid structure 102 and the actuation structure 108. Forinstance, in some cases the rigid structure 102 and the actuationstructure 108 may each include one or more magnets, such that themagnets have an attractive force that pulls the rigid structure 102 andthe actuation structure 108 towards one another.

Irrespective of how the restorative mechanism applies force to the buildsurface, according to some embodiments, the restorative mechanism mayapply force to the build surface such that there is no substantialdeformation of the build surface away from the rigid body duringadditive fabrication process. That is, forces applied by the restorativemechanism to the build surface may be sufficiently high to overcomeforces applied to the build surface in an opposing direction duringfabrication (e.g., the downward force experienced by the build surfaceresulting from pulling a fabricated part from liquid resin).

In some embodiments, the flexible sheet 112 may be attracted and/orattached to the rigid structure 102 by restorative mechanism using anynumber of techniques, including magnetic, vacuum, adhesive and/ormechanical forces. In some embodiments in which a build surfacecomprises one or more ferromagnetic materials, a restorative mechanismmay preferably comprise one or more magnets, such as one or more sheetmagnets.

In some embodiments, actuation of the sheet handles 110 may result in aprogressive “peeling” of the flexible sheet 112 away from the rigidstructure 102 that begins at the center of the flexible sheet 112 andprogresses across the rigid body towards edges of the flexible sheet112. This progressing peeling may tend to cause the build layer to adopta bend at the propagating separation boundary, thereby potentiallyseparating a part from the build layer.

FIGS. 2A-2C illustrate components of the actuation structure 108 of thebuild platform 100 suitable for use in an additive fabrication device,according to some embodiments. In the example of FIGS. 2A-2C, theactuation structure 108 is configured to deform (e.g., flex at theflexible sheet 112) through the application of force at the sheethandles 110 while the actuation structure 108 is attached to the rigidstructure 102 (FIGS. 1A-1C), or as a stand-alone device. The actuationstructure 108 includes the flexible sheet 112 fixedly attached to thesheet handles 110 at opposite edges. In some embodiments, the flexiblesheet 112 may be comprise, or may consist of, one or more ferromagneticmaterials or may be coated in one or more ferromagnetic materials. Insome embodiments, the flexible sheet 112 may be formed of a sufficientlyrigid material that the material exerts a restorative force when thesheet is deformed. In some embodiments, the flexible sheet 112 has ashape and size substantially similar to that of the bottom surface ofrigid structure 102, and can be attached to rigid structure 102 throughmagnetic attraction (e.g., the rigid structure 102 includes one or moremagnets on or below its bottom surface). In some embodiments, the sheethandles 110 are joined to flexible sheet 112 at the bottom of thehandles by welding, glue, fasteners, or other means (e.g., the handlerods 116 are attached to the flexible sheet 112).

FIG. 2B illustrates the sheet handle 110 of the actuation structure 108.In some embodiments, the sheet handle 110 is attached to the flexiblesheet 112 along an edge of the flexible sheet 112. The sheet handle 110includes a handle frame 202, a handle rod 116, and a handle body 204. Insome embodiments, the handle rod 116 is attached to the handle frame 202by welding, glue, fasteners, or other means. The handle rod 116 maycomprise, or may consist of, one or more ferromagnetic materials or maybe coated in one or more ferromagnetic materials.

FIG. 2C shows a detailed view of the handle rod 116. In someembodiments, the handle rod 116 has a flat bottom surface and a roundedtop surface. As a result, the cross-section of the handle rod 116resembles a segment of a circle. In some embodiments, the rounded topsurface makes sliding contacts with the trough 114 of the rigidstructure 102 (FIGS. 1A-1C) during the actuation of the actuationstructure 118, thereby enables the sheet handle 110 to pivot around thehandle rod 116. As will be described in more detail below (e.g., FIG. 4), in some embodiments, magnets are embedded in the rigid structureabove the troughs 114 to attract the handle rods 116 to the troughs ofthe rigid structure 102.

FIGS. 3A-3C illustrate the rigid structure 102 of build platform 100 indifferent perspectives, according to some embodiments.

FIG. 3A shows a cross-sectional view of the rigid structure 102,according to some embodiments. In the example of FIG. 3A, the rigidstructure 102 includes a top surface 302 and a bottom surface 304. Thetop handle 106 (e.g., as shown in FIG. 1A) is attached to the topsurface 302 at a center portion. In some embodiments, recess regions 306(also known as “cams”) are formed within the top surface 302 andpositioned on either side of the top handle 106. As will be described inmore detail below, the recess regions 306 may serve as guides for thesheet handles 110 during actuation (“actuation” is defined as causingthe one or both sheet handles 110 to move (e.g., rotating, bendingand/or moving laterally) towards the top handle 106, such as by pushingthe sheet handles 110 manually or by motorized means), wherein duringactuation the sheet handles make contact with the recess region 306. Asa result of this guided motion, the actuation structure 108 may maintaincontact with the rigid structure 102 during the actuation.

In the example of FIGS. 3A-3C, the bottom surface 304 of the rigidstructure 102 includes a substantially flat center portion for attachingto the flexible sheet 112. The bottom surface 304 also includes troughs114 arranged at opposing sides of the rigid structure that engage withthe handle rods 116. The troughs 114 may be formed with any suitablecross-sectional shape that limits the movement of the handle rods 116during at least part of actuation. For example, the troughs 114 mayinclude a curved surface, a delta-gap shaped surface, a slanted surface,etc. In some embodiments, the troughs 114 may be configured to have across-sectional shape that matches the cross-sectional shape of thehandle rods, so in at least one position the handle rods can sit fullywithin the troughs. During actuation, the handle rods may rotate orotherwise move within the troughs, with the trough and handle rods'cross-sectional shapes dictating the motion of the flexible sheet thatresults from the motion of the handle rod against the trough.

As will be described in more detail in FIGS. 5A-5D, during actuation ofthe actuation structure 108, the sheet handles 110 may travel towardseach other by sliding along the recess regions 306, and during this timethe handle rods 116 may stay within or substantially within the troughs114 to allow the flexible sheet 112 to deform. In some embodiments, therecess regions 306 have a shape and depth that correspond to thegeometry of the sheet handles 110 such that during actuation, the handlerods 116 are able to stay within or substantially within the troughs114.

FIG. 3B shows a bottom view of the bottom surface 304 of the rigidstructure 102, according to some embodiments. In the example of FIG. 3B,the view is a partially transparent one with features of the rigidstructure other than the bottom surface 304 shown in light gray todepict their position for purposes of illustration. Though, it will beappreciated that these features may not be visible from the bottom ofthe rigid structure in practice.

In the example of FIG. 3B, the bottom surface 304 includes at least twotypes of magnetic zones: a face magnetic zone 308 in the center of thebottom surface 304 exerting a first amount of magnetic force per unitarea towards the center portion of the flexible sheet 112, and edgemagnetic zones 310 along the edges (e.g., the edges where the sheethandles 110 are located) exerting a second amount of magnetic force perunit area towards the edge portions (e.g., the handle rods 116) of theflexible sheet 112. In some embodiments, the second amount is greaterthan the first amount, so that the edges apply a greater magnetic forceby unit area than does the center portion.

As a result of the magnetic zones applying a different magnitude ofmagnetic force, during actuation the flexible sheet 112 may separate(e.g., peel off the rigid structure 102) from the bottom surface 304 ofthe rigid structure 102 in a progressive manner. For example, the centerportion of the flexible sheet may first separate from the bottomsurface, then as the actuation continues and the force applied to theflexible sheet increases, the flexible sheet 112 and the bottom surface304 separate from the edges of the rigid structure. In some embodiments,during actuation, due to the troughs 114 engaging with the handle rods116, the recess regions 306 engaging with the sheet handles 110, and thetop handle 106 serving as a stopper, the actuation structure 108 stayson the rigid structure 102 throughout the duration of the actuation.

FIG. 3C is a cross-sectional view of the rigid structure, showing anillustrative placement of magnets within the structure, according tosome embodiments. In the example of FIG. 3C, an arranged group ofindividual magnets (e.g., an N×N array of magnets) and/or a sheet magnet312 is located within the rigid structure and above the bottom surface304 to create the face magnetic zone 308 discussed above in relation toFIG. 3B. One or more magnets 314 may be arranged within or adjacent tothe trough 114 to create each edge magnetic zone 310. In someembodiments, the magnets are heat sealed within the rigid structure 102.

FIG. 4 illustrates an exemplary design of the trough 114 on the rigidstructure 102, according to some embodiments. The top surface of thehandle rods 116 and the troughs 114 have corresponding shape to allowengagement. As shown in FIG. 4 , each handle rod 116 has a curved topsurface that engages with the trough 114, which has a correspondingcurved surface. As the handle rod 116 sits within the trough 114, theflexible sheet 112 also sits flush against the center portion of thebottom surface 304 of the rigid structure 102. In some embodiments, thetrough 114 is slightly larger than the handle rod 116, resulting in gap402 and gap 404 between the handle rod and the trough. In at least somecases, the gap 404 may allow for misalignment between the trough 114 andthe handle rod 116. In at least some cases, the gap 402 may allow thehandle rod 116 to move towards the walls of the rigid structure duringactuation. As an alternative to the illustrative cross-sectional shapeshown in FIG. 4 , the handle rod 116 may instead have a flat top surface(e.g., rectangular cross-section view) or a slanted top surface (e.g.,triangular cross-section view). In such cases, the troughs 114 may havea corresponding shape (e.g., delta-gap or slanted).

In the example of FIG. 4 , as the sheet handle 110 actuates, theflexible sheet 112 flexes away from the bottom surface 304 of the rigidstructure 102. The handle rod 116 shown in FIG. 4 turns counterclockwise(whereas the other handle rod 116 on the other side of the flexiblesheet 112 will turn in the opposite direction) and moves towards the gap404. More discussion on the movement of the sheet handles 110 duringactuation is described below with respect to FIGS. 5A-5D.

FIGS. 5A-5D illustrate an exemplary process in which the actuationstructure 108 actuates to release fabricated parts from the buildplatform 100, according to some embodiments.

In FIG. 5A, rigid structure 102 is attached to the actuation structure108 (e.g., via magnetic attraction between the flexible sheet 112 andmagnets within the rigid structure), with the flexible sheet 112 sitsflush against the bottom surface 304 of the rigid structure 102. Thesheet handles 110 abut either side of the rigid structure 102. Toactuate the sheet handles, a force is exerted on one or both sheethandles 110 towards the top handle 106. For example, a user may applythe force single-handedly by holding on the top handle 106 with fingersand pushing the sheet handle 110 towards the top handle 106 with theuser's palm or thumb. In another example, the user may hold the buildplatform 110 by grabbing both sheet handles 110 with two hands, andsqueeze the sheet handles 110. In another example, the build platform100 may be mounted on a device (e.g., the mount shown in FIG. 6 , awashing station, a curing station, or an additive fabrication device)using the mounting attachment 104 (FIG. 1A) for a user to apply theforce. In another example, instead of manually operating the actuationstructure 108, the user may rely on a motorized device to push one orboth of the sheet handles 110.

FIG. 5B shows the actuation structure 108 during actuation, as the useror a motorized device pushes at least one of the sheet handles 110towards the top handle 106. When the actuation first starts, theflexible sheet 112 of the actuation structure 108 may be subjected toone or more forces, which may include any one or more of: (1) aseparation force due to the actuation of the sheet handle 110 thatpushes the flexible sheet 112 away from the bottom surface 304 of therigid structure 102; (2) an elastic restoring force that tends toflatten the flexible sheet 112, which in turn pushes the flexible sheet112 towards the bottom surface 304 to stay flat; (3) a first magneticforce exerted on a central portion of the flexible sheet 112 from theface magnetic zone 308 (FIG. 3B) of the rigid structure 102, whichpushes the flexible sheet 112 towards the bottom surface 304; (4) asecond magnetic force exerted on edge portions of the flexible sheet 112by the edge magnetic zone 310 (FIG. 3B) that pushes the flexible sheettowards the bottom surface 304, and (5) a normal force exerted on thehandle rods 116 by the troughs 114, that limits the movement of thehandle rods 116 to substantially within the troughs 114.

At a first point in time during the actuation, the sheet handles 110travel a first distance and the separation force may be weak compared tothe attraction force. As a result, the flexible sheet 112 may stay flaton the bottom surface 304.

At a second point in time during the actuation, the sheet handles 110travel a second distance (e.g., greater than the first distance) and theseparation force causes a center portion of the flexible sheet 112 toseparate from the bottom surface 304.

At a third point in time during the actuation, the sheet handles 110travel a third distance (e.g., greater than the second distance, or allthe way to come into contact with the top handle 106 as the maximumdistance allowed), which causes the separation between the flexiblesheet 112 and the bottom surface 304 to progress towards the edges(e.g., peeling). As a result, the separation between the flexible sheet112 and the bottom surface 304 become larger.

According to some embodiments, during the actuation of the sheet handles110 the sheet handles may make sliding contact with the recess region306 on the top surface 302 of the rigid structure 102. The handle rods116 stay engaged with the troughs 114 and are limited to move within thetroughs 114. As a result, the actuation structure 108 stays on the rigidstructure 102 throughout the actuation.

FIG. 5D shows that, in some embodiments, after the application of forceceases, the group of attraction forces causes the flexible sheet 112 torestore to its original configuration and returns to sitting flushagainst the bottom surface 304 of the rigid structure 102.

FIGS. 6A-6B illustrate an exemplary mount 600 (also known as a “jig”) onwhich the build platform 100 can be mounted for removing fabricatedparts 602. For example, the mount 600 can be secured at one end to asurface (e.g., tabletop), and attaches to the build platform 100 at themounting attachment 104 (FIG. 1A). In some embodiments, the mount 600can be adjusted to orient at different angles. For example, the mount600 can be oriented such that the build platform 100 is facing upward(as shown in FIGS. 6A-6B), or is facing at an angle. The actuation ofthe build surface (e.g., as described in FIGS. 5A-5D) allows theflexible sheet 112 to deform and release fabricated parts stuck on theflexible sheet 112.

FIGS. 7A-7I illustrate exemplary dripping-prevention structures 700 onthe sheet handles 110, according to some embodiments. When the buildplatform 100 is removed from the additive fabrication device (e.g., theadditive fabrication device in FIGS. 8A-8B) after a fabrication session,uncured liquid resin may remain on the flexible sheet 112 or on thefabricated parts (not shown in FIGS. 7A-7D). The uncured liquid resinmay drip down the sheet handles 110 when a user operates the buildplatform 100, causing chemical hazard risks to the user. Each of theillustrative dripping-prevention structures 700 shown in FIGS. 7A-7I arestructures that catch or otherwise break the flow path of uncured liquidresin dripping from the flexible sheet 112 to inhibit the liquid fromspilling from the build platform and/or from reaching the handle of thebuild platform.

In the example of FIG. 7A, the sheet handles 110 of build platform 100include sections 700 having the shape of an upward-facing bowl that maycatch liquid resin spilling from the build surface. The upward-facingbowl shape is shown in cross-section in inset 702. Other illustrativedripping-prevention structures are shown in cross-sections 704, 706 and708, and illustrate protrusions that break the flow path of resin fromthe flexible sheet 112 to falling from the build platform.

Other illustrative dripping-prevention structures include a kink 710 inthe sheet handles 110 (as shown in FIG. 7B), cuts 712 in the sheethandles (as shown in FIG. 7C). Also pictured are multi-piece handledesigns 714, 716 and 718 (shown in FIGS. 7D, 7E and 7F, respectively),and grips 724 (shown in FIG. 7I).

In the example of FIGS. 7G and 7H, a skirt is arranged attached to thesheet handles 110. In the case of skirt 720 shown in FIG. 7G, astructure (which may be flexible or rigid) is coupled between the topbar of a sheet handle and the top surface of the rigid structure 102.This skirt structure therefore inhibits resin from spilling off theflexible sheet 112 of the build platform and falling through the gapbetween the sheet handle and the build platform, when the build platformis oriented as shown in FIG. 7G. Instead, the skirt may catch the resinon its surface.

In the case of skirt 722 shown in FIG. 7H, a structure (which may beflexible or rigid) is coupled around the edge of the rigid structure 102and sheet handles 110. This skirt structure therefore inhibits resinfrom spilling off the flexible sheet 112 of the build platform andfalling beneath the build platform, when the build platform is orientedas shown in FIG. 7H. Instead, the skirt may catch the resin on itssurface.

FIGS. 8A-8B depict an illustrative additive fabrication devicecomprising a build platform configured as per any of the embodimentsdiscussed above. Illustrative stereolithographic printer 800 comprises asupport base 801, a display and control panel 808, and a reservoir anddispensing system 804 for storage and dispensing of photopolymer resin.The support base 801 may contain various mechanical, optical,electrical, and electronic components that may be operable to fabricateobjects using the system. During operation, photopolymer resin may bedispensed from the dispensing system 804 into container 802.

Build platform 805 may be positioned along a vertical axis 803 (orientedalong the z-axis direction as shown in FIGS. 7A-7B) such that the bottomfacing layer (lowest z-axis position) of an object being fabricated, orthe bottom facing layer of build platform 805 itself, is a desireddistance along the z-axis from the bottom 811 of container 802. Thedesired distance may be selected based on a desired thickness of a layerof solid material to be produced on the build platform or onto apreviously formed layer of the object being fabricated. In the exampleof FIGS. 8A-8B, the build surface of the build platform 805 faces in the−z direction, towards the container 802.

According to some embodiments, build platform 100 as shown in FIG. 1Amay be employed in system 800 as build platform 805. In someembodiments, the build platform 805 may be removable from the printer800. For instance, the build platform 805 may be attached to arm 815(e.g., pressure fit or fastened onto) and may be removed from theprinter so that a part attached to the build surface can be removed viathe techniques described above.

In the example of FIGS. 8A-8B, the bottom 811 of container 802 may betransparent to actinic radiation that is generated by a radiation source(not shown) located within the support base 801, such that liquidphotopolymer resin located between the bottom 811 of container 802 andthe bottom facing portion of build platform 805 or an object beingfabricated thereon, may be exposed to the radiation. Upon exposure tosuch actinic radiation, the liquid photopolymer may undergo a chemicalreaction, sometimes referred to as “curing,” that substantiallysolidifies and attaches the exposed resin to the bottom facing portionof build platform 805 or to an object being fabricated thereon. FIGS.8A-8B represent a configuration of stereolithographic printer 801 priorto formation of any layers of an object on build platform 805, and forclarity also omits any liquid photopolymer resin from being shown withinthe depicted container 802.

Following the curing of a layer of material, build platform 805 may bemoved along the vertical axis of motion 803 in order to reposition thebuild platform 805 for the formation of a new layer and/or to imposeseparation forces upon any bond with the bottom 811 of container 802. Inaddition, container 802 is mounted onto the support base such that thestereolithographic printer 801 may move the container along horizontalaxis of motion 810, the motion thereby advantageously introducingadditional separation forces in at least some cases. A wiper 806 isadditionally provided, capable of motion along the horizontal axis ofmotion 810 and which may be removably or otherwise mounted onto thesupport base at 809.

FIG. 9 depicts an illustrative selective laser sintering (SLS) additivefabrication device comprising a build platform configured as per any ofthe embodiments discussed above. In the example of FIG. 9 , SLS device900 comprises a laser 910 paired with a computer-controlled scannersystem 915 disposed to operatively aim the laser 910 at the fabricationbed 930 and move over the area corresponding to a given cross-sectionalarea of a computer aided design (CAD) model representing a desired part.Suitable scanning systems may include one or more mechanical gantries,linear scanning devices using polygonal mirrors, and/orgalvanometer-based scanning devices.

In the example of FIG. 9 , the material in the fabrication bed 930 isselectively heated by the laser in a manner that causes the powdermaterial particles to fuse (sometimes also referred to as “sintering” or“consolidating”) such that a new layer of the object 940 is formed. SLSis suitable for use with many different powdered materials, includingany of various forms of powdered nylon. In some cases, areas around thefabrication bed (e.g., the walls 932, the platform 931, etc.) mayinclude heating elements to heat the powder in the fabrication bed. Suchheaters may be used to preheat unconsolidated material, as discussedabove, prior to consolidation via the laser.

Once a layer has been successfully formed, the build platform 931 may belowered a predetermined distance by a motion system (not pictured inFIG. 9 ). Once the build platform 931 has been lowered, the materialdeposition mechanism 925 may be moved across the fabrication bed 930,spreading a fresh layer of material across the fabrication bed 930 to beconsolidated as described above. Mechanisms configured to apply aconsistent layer of material onto the fabrication bed may include theuse of wipers, rollers, blades, and/or other levelling mechanisms formoving material from a source of fresh material to a target location.

According to some embodiments, build platform 100 as shown in FIG. 1Amay be employed in system 900 as build platform 931. In someembodiments, the build platform 931 may be removable from the system900.

Since material in the powder bed 930 is typically only consolidated incertain locations by the laser, some material will generally remainwithin the bed in an unconsolidated state. This unconsolidated materialis sometimes referred to as a “part cake.” In some embodiments, the partcake may be used to physically support features such as overhangs andthin walls during the formation process, allowing for SLS systems toavoid the use of temporary mechanical support structures, such as may beused in other additive manufacturing techniques such asstereolithography. In addition, this may further allow parts with morecomplicated geometries, such as moveable joints or other isolatedfeatures, to be fabricated with interlocking but unconnected components.

The above-described process of producing a fresh layer of powder andconsolidating material using the laser repeats to form an objectlayer-by-layer until the entire object has been fabricated. Once theobject has been fully fabricated, the object and the part cake may becooled at a controlled rate so as to limit issues that may arise withfast cooling, such as warping or other distortion due to variable ratecooling. The object and part cake may be cooled while within theselective laser sintering apparatus, or removed from the apparatus afterfabrication to continue cooling. Once fully cooled, the object can beseparated from the part cake by a variety of methods. The unusedmaterial in the part cake may optionally be recycled for use insubsequent fabrication.

According to some embodiments, a computer system may be providedsuitable for generating instructions to perform additive fabrication byan additive fabrication device comprising a removable build platform(e.g., build platform 100, 120, 140 or 200, as shown in FIGS. 1A, 1B, 1Cand 2A-2C, respectively). The computer system may execute software thatgenerates two-dimensional layers that may each comprise sections of theobject. Instructions may then be generated from this layer data to beprovided to an additive fabrication device, that, when executed by thedevice, fabricates the layers and thereby fabricates the object. Suchinstructions may be communicated to the additive fabrication device viaany suitable wired and/or wireless communications connection. In someembodiments, a single housing may hold the computing device and theadditive fabrication device such that the link is an internal linkconnecting two modules within the housing of the system.

According to some embodiments, it may be beneficial to both increase thestability and/or adhesion of a fabricated part to a build layer and toimprove the removability of the part by forming a structure, known as a“raft,” on the build layer (e.g., prior to forming the first layer ofthe body of the part). As discussed in U.S. patent application Ser. No.14/501,967, titled “Systems and Methods of Post-Processing Features forAdditive Fabrication,” filed on Sep. 30, 2014, which is herebyincorporated by reference in its entirety, such a raft structure may beadded to the part for fabrication and subsequently removed inpost-processing steps to leave only the desired part.

In some embodiments, a computer system configured to generateinstructions to perform additive fabrication may optimize a raftstructure in order to increase the effectiveness of part removal via theuse of a removal mechanism or other means of distorting the build layerIn particular, as discussed above, the forces applied against the baseof a part attached to a build layer depend in part on the relationshipof the radius of curvature of a bend in the build layer and thedimension of the part base along the axis of the bend. Accordingly, insome embodiments a computer system configured to generate instructionsto perform additive fabrication may generate raft structures having alength configured to be greater along the bend axis of the buildplatform, in order to increase the degree of force applied to the raftduring the removal process.

In some embodiments, a computer system configured to generateinstructions to perform additive fabrication may generate a raftstructure by taking into account a desired rigidity in a direction alongthe axis of the bend in the build layer during removal of a part. Forexample, the computer system may optimize a raft structure by increasingthe rigidity of the structure against bending forces in the axis of thebend in the build layer. Such increases in rigidity may advantageouslyincrease the amount of force potentially exerted between the bend in thebuild layer and the raft structure attaching the part to the buildlayer. For instance, generation of the raft by the computer system toincrease strength, such as by forming thicker regions, ribbing, or otherreinforcing structures, may help to counter this tendency, particularlyin instances wherein the build material may be comparatively flexible orhave low tensile strength.

In some instances, it may be further advantageous to conductpost-processing steps, such as thermal or actinic post curing of “greenparts,” appropriate to increase material strength or other propertiesprior to the application of removal forces. Alternatively, infabrication technologies utilizing multiple or variable propertymaterials, it may be advantageous to form one or more raft layers ofmaterials having increased rigidity and strength as compared to one ormore regions of the part.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated that various alterations,modifications, and improvements will readily occur to those skilled inthe art.

Such alterations, modifications, and improvements are intended to bepart of this disclosure, and are intended to be within the spirit andscope of the invention. Further, though advantages of the presentinvention are indicated, it should be appreciated that not everyembodiment of the technology described herein will include everydescribed advantage. Some embodiments may not implement any featuresdescribed as advantageous herein and in some instances one or more ofthe described features may be implemented to achieve furtherembodiments. Accordingly, the foregoing description and drawings are byway of example only.

Various aspects of the present invention may be used alone, incombination, or in a variety of arrangements not specifically discussedin the embodiments described in the foregoing and is therefore notlimited in its application to the details and arrangement of componentsset forth in the foregoing description or illustrated in the drawings.For example, aspects described in one embodiment may be combined in anymanner with aspects described in other embodiments.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

The terms “approximately” and “about” may be used to mean within ±20% ofa target value in some embodiments, within ±10% of a target value insome embodiments, within ±5% of a target value in some embodiments, andyet within ±2% of a target value in some embodiments. The terms“approximately” and “about” may include the target value. The term“substantially equal” may be used to refer to values that are within±20% of one another in some embodiments, within ±10% of one another insome embodiments, within ±5% of one another in some embodiments, and yetwithin ±2% of one another in some embodiments.

The term “substantially” may be used to refer to values that are within±20% of a comparative measure in some embodiments, within ±10% in someembodiments, within ±5% in some embodiments, and yet within ±2% in someembodiments. For example, a first direction that is “substantially”perpendicular to a second direction may refer to a first direction thatis within ±20% of making a 90° angle with the second direction in someembodiments, within ±10% of making a 90° angle with the second directionin some embodiments, within ±5% of making a 90° angle with the seconddirection in some embodiments, and yet within ±2% of making a 90° anglewith the second direction in some embodiments.

Also, the phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having,” “containing,” “involving,” andvariations thereof herein, is meant to encompass the items listedthereafter and equivalents thereof as well as additional items.

What is claimed is:
 1. A build platform configured to be removablyattached to an additive fabrication device, the build platformcomprising: a rigid structure; and an actuation structure coupled to therigid structure and comprising one or more sheet handles and a flexiblesheet, wherein the one or more sheet handles are attached to theflexible sheet, wherein a first surface of the flexible sheet forms abuild surface on which the additive fabrication device is configured toform layers of material, and wherein the one or more sheet handles areconfigured to be actuated to deform at least a part of the flexiblesheet away from the rigid structure.
 2. The build platform of claim 1,further comprising one or more magnets that couple the actuationstructure to the rigid structure.
 3. The build platform of claim 2,wherein a second surface of the flexible sheet is configured to becoupled to a first surface of the rigid structure, and wherein the firstsurface of the rigid structure includes: a first magnetic zone exertinga first amount of magnetic force per area on the actuation structure,and a second magnetic zone exerting a second mount of magnetic force perarea on the actuation structure; and wherein the first amount isdifferent from the second amount.
 4. The build platform of claim 1,wherein the one or more sheet handles include two sheet handles attachedto the flexible sheet at opposite sides of the flexible sheet.
 5. Thebuild platform of claim 1, wherein the rigid structure includes amounting device configured to be removably attached to the additivefabrication device.
 6. The build platform of claim 1, wherein the one ormore sheet handles each comprises a drip-prevention structure to catchliquid that drips from the flexible sheet when the build platform isoriented with the flexible sheet above the one or more sheet handles. 7.The build platform of claim 1, wherein the build platform is configuredto be removed from the additive fabrication device and to be removablyattached to a mount for the actuation of the one or more sheet handles.8. The build platform of claim 1, wherein the rigid structure includesone or more troughs at its edges, and wherein a part of each of the oneor more sheet handles rests in one of the one or more troughs.
 9. Thebuild platform of claim 1, wherein during actuation of the one or moresheet handles to apply a force to the flexible sheet: during a firstphase of the actuation, an elastic force experienced by a first part ofthe flexible sheet is smaller than the magnetic force exerted on thefirst part of the flexible sheet; during a second phase of theactuation, the elastic force experienced by the first part of theflexible sheet is greater than the magnetic force exerted on the firstpart of the flexible sheet.
 10. The build platform of claim 1, whereinthe one or more sheet handles are configured to be actuated while atleast a part of the actuation structure remains attached to the rigidstructure.
 11. The build platform of claim 1, wherein the actuationstructure is coupled to the rigid structure through mechanical retainingmeans.
 12. An additive fabrication device configured to form layers ofmaterial on a build surface, the additive fabrication device comprising:a build platform comprising: a rigid structure; and an actuationstructure coupled to the rigid structure and comprising one or moresheet handles and a flexible sheet, wherein the one or more sheethandles are attached to the flexible sheet, wherein a first surface ofthe flexible sheet forms a build surface on which the additivefabrication device is configured to form layers of material, and whereinthe one or more sheet handles are configured to be actuated to deform atleast a part of the flexible sheet away from the rigid structure. 13.The additive fabrication device of claim 12, wherein the build platformfurther comprises one or more magnets that couple the actuationstructure to the rigid structure.
 14. The additive fabrication device ofclaim 13, wherein a second surface of the flexible sheet is configuredto be coupled to a first surface of the rigid structure, and wherein thefirst surface of the rigid structure includes: a first magnetic zoneexerting a first amount of magnetic force per area on the actuationstructure, and a second magnetic zone exerting a second mount ofmagnetic force per area on the actuation structure; and wherein thefirst amount is different from the second amount.
 15. The additivefabrication device of claim 12, wherein the one or more sheet handlesinclude two sheet handles attached to the flexible sheet at oppositesides of the flexible sheet.
 16. The additive fabrication device ofclaim 12, wherein the rigid structure includes a mounting deviceconfigured to be removably attached to the additive fabrication device.17. The additive fabrication device of claim 12, wherein the one or moresheet handles each comprises a drip-prevention structure to catch liquidthat drips from the flexible sheet when the build platform is orientedwith the flexible sheet above the one or more sheet handles.
 18. Theadditive fabrication device of claim 12, wherein the build platform isconfigured to be removed from the additive fabrication device and to beremovably attached to a mount for the actuation of the one or more sheethandles.
 19. The additive fabrication device of claim 12, wherein therigid structure includes one or more troughs at its edges, and wherein apart of each of the one or more sheet handles rests in one of the one ormore troughs.
 20. The additive fabrication device of claim 12, whereinduring actuation of the one or more sheet handles to apply a force tothe flexible sheet: during a first phase of the actuation, an elasticforce experienced by a first part of the flexible sheet is smaller thanthe magnetic force exerted on the first part of the flexible sheet;during a second phase of the actuation, the elastic force experienced bythe first part of the flexible sheet is greater than the magnetic forceexerted on the first part of the flexible sheet.
 21. The additivefabrication device of claim 12, wherein the one or more sheet handlesare configured to be actuated while at least a part of the actuationstructure remains attached to the rigid structure.
 22. The additivefabrication device of claim 12, wherein the actuation structure iscoupled to the rigid structure through mechanical retaining means.